This invention relates to a holographic reconstructing apparatus, and more particularly to a holographic reconstructing apparatus capable of exchanging hologram plates and having a large memory capacity.
Conventionally in a holographic reconstructing apparatus using a hologram, even if the position of a laser beam deviates more or less from the position of a hologram memory plate, due to a redundancy of the hologram, all the required information can still be reproduced. Therefore, a small addressing inaccuracy has been allowed for a laser beam which irradiates, via a light deflector, a hologram memory plate. However, in order to store a large number of pieces information in a high density in one sheet of hologram plate, it has become necessary to use a Fourier transform type hologram, and to make the hologram small sized and in a high density. As a result, it has become necessary to make a drift of the many hologram address positions of a light beam small which drift arises from external noise in the reconstructing means such as the variation of the laser beam in the exit angle of the laser source.
There is a limit in recording a large quantity of information on a sheet of hologram plate, and it is apparent that it is possible to make recording and reconstruction of a large quantity of information by exchanging a plurality of hologram memory plates and reconstructing. However, exchange of the plates requires a high precision in the spatial position of the plate itself as well as in the relative position between a hologram memory plate and each recorded hologram and a certain type of servo mechanism is required. However, it has been difficult to attain a high speed control of the position of the hologram plate since the mass of the hologram plate itself is large.